Printer calibration

Abstract

A system and method for calibrating a printer includes the steps or functions of: printing a predetermined color test pattern with the printer by transforming data, representing said predetermined color test pattern, from a device-independent color space to a device-dependent color space associated with the printer by use of a color transform, said predetermined color test pattern including a set of color patches with one of said color patches representing a preferred mid-gray hue; providing a predetermined reference gray surface; comparing said reference gray surface to said set of colored patches of the printed test pattern to find a closest matching one of said patches, if the closest matching one of said patches is the patch representing the preferred mid-gray hue, then ending the method; otherwise determining, for each color channel of the printer, a solution set of correction values as a function of believed gray versus actual gray, said solution set derived from and including a white point, a black point and a point mapped at {G b , G a } where G b is the believed gray value of the closest matching one of said patches and G a is the actual gray value of the closest matching one of said patches; and adding to the color transform the corresponding solution set for each color channel of the printer.

We claim: 
     
       1. A method for improving a color transform for a printer comprising the steps of: transforming predetermined data, representing a color test pattern, into a digital image in a device-dependent color space associated with the printer by use of a test pattern transform, said test pattern transform comprising a portion of the color transform pertaining to the printer coupled with any solution set formed by a previous instantiation of said method, wherein said color test pattern data includes a set of color patches in a device-independent color space with one of said color patches representing a preferred mid-gray hue and other patches representing colors that are close to said preferred mid-gray hue in said device-independent color space;   printing said digital image to create a printed color test pattern;   providing a reference gray surface having a spectral reflectance characteristic that is flat or nearly flat and a gray level that is the same as said preferred mid-gray hue;   comparing said reference gray surface to said set of colored patches of the printed test pattern to find a closest matching one of said patches, if the closest matching one of said patches is the patch representing the preferred mid-gray hue, then ending the method; otherwise   storing a data set of values indicative of the closest matching one of said colored patches;   determining, for each color channel of the printer, a solution set of correction values as a function of believed values versus actual values, said solution set derived from and including a point {0,0}, a point {1.0,1.0}, whereby the maximum printer device value is normalized to 1.0, and a point mapped at {G b , G a  } where G b  is the believed value of the closest matching one of said patches and G a  is the actual value of the closest matching one of said patches;   adding to the color transform the corresponding solution set for each color channel of the printer; and   repeating this method using the color transform having the corresponding solution set added thereto.   
     
     
       2. The method of claim 1 wherein, in CIELAB values, said reference gray surface measures {50,0,0}. 
     
     
       3. The method of claim 1 wherein the color transform is facilitated by use of a pair of profiles and said portion of the color transform pertaining to the printer is given by the printer profile. 
     
     
       4. A system for improving a color transform for a printer comprising: means for transforming predetermined data, representing a color test pattern, into a digital image in a device-dependent color space associated with the printer by use of a test pattern transform, said test pattern transform comprising a portion of the color transform pertaining to the printer coupled with any solution set formed by a previous instantiation of said method, wherein said color test pattern data includes a set of color patches in a device-independent color space with one of said color patches representing a preferred mid-gray hue and other patches representing colors that are close to said preferred mid-say hue in said device-independent color space;   means for printing said digital image to create a printed color test pattern:   means for comparing a reference gray surface, having a spectral reflectance characteristic that is flat or nearly flat and a gray level that is the same as said preferred mid-gray hue, to said set of colored patches of the test pattern rendered by the printer to find a closest matching one of said patches, ceasing operation if the closest matching one of said patches is the patch representing the preferred mid-gray hue;   means for storing a data set of values indicative of the closest matching one of said colored patches;   means for determining, for each color channel of the printer, a solution set of correction values as a function of believed values versus actual values, said solution set derived from and including a point {0,0}, a point {1.0, 1.0}, whereby the maximum printer device value is normalized to 1.0, and a point mapped at {G b , G a  } where G b  is the believed value of the closest matching one of said patches and G a  is the actual value of the closest matching one of said patches;   means for adding to the color transform the corresponding solution set for each color channel of the printer; and   means for restarting the system using the color transform having the corresponding solution set added thereto.   
     
     
       5. The system of claim 4 wherein, in CIELAB values, said reference gray surface measures {50,0,0}. 
     
     
       6. The system of claim 4 wherein the color transform is facilitated by use of a pair of profiles and said portion of the color transform pertaining to the printer is given by the printer profile. 
     
     
       7. The method of claim 1 wherein the process of adding the corresponding solution set to the color transform for each color channel of the printer is accomplished by concatenating the solution set with the color transform. 
     
     
       8. The method of claim 1 wherein the process of adding the corresponding solution set to color transform for each color channel of the printer is accomplished by creating lookup tables from the solution set and modifying the output of the color transform using said lookup tables. 
     
     
       9. The method of claim 1 wherein the process of adding the corresponding solution set to the color transform for each color channel of the printer is accomplished by creating lookup tables from the solution set and downloading said lookup tables to the printer. 
     
     
       10. The system of claim 4 wherein the means for adding the corresponding solution set to the color transform for each color channel of the printer is accomplished by concatenating the solution set with the color transform. 
     
     
       11. The system of claim 4 wherein the means for adding the corresponding solution set to color transform for each color channel of the printer is accomplished by creating lookup tables from the solution set and modifying the output of the color transform using said lookup tables. 
     
     
       12. The system of claim 4 wherein the means for adding the corresponding solution set to the color transform for each color channel of the printer is accomplished by creating lookup tables from the solution set and downloading said lookup tables to the printer.